Downdraft Biomass Gasification: Experimental Investigation and Aspen Plus Simulation

Abstract

Biomass gasification is considered today as a promising route for energy production, including electricity, natural gas or synthetic biofuels. Mechanisms involved in such processes are very complex and need further understanding. In downdraft gasification processes, the gasification dynamics is fundamental to the energy efficiency and the quality of gas produced. The focus of this work is to provide necessary data for development and validation of 2D CFD codes to investigate the behaviour of the gasification zone of a downdraft gasifier. For this, two major set of experiments were performed: Char Gasification in A Continuous Fixed Bed Reactor – CfiBR: The experiments were performed in a cylindrical reacting char bed and measurements of pressure drop, gas composition (longitudinal direction) and temperature (radial and longitudinal directions) were made. The char bed height was kept to 65 cm and the product gas was extracted through the bottom of the reactor and taken to a combustion chamber for final oxidation, after passing through a cyclone which separates the fine particles. Profiles of gas composition and temperature are presented for two different inlet gas compositions. Gasification in a 25kw Throated Fixed Bed Biomass Gasifier: a commercially available 25kg/h throated reactor was modified to be able to measure pressure drop, gas composition (longitudinal direction) and temperature (radial and longitudinal directions). The device consists of a metallic reactor (280mm id, 76.2mm throat) surrounded by refractory insulation. An auger enables the feeding of biomass to the top of the reactor. The biomass flow rate is controlled by the consumption of the reactor. Air inlet and gas outlet are both measured using orifice plates installed in the device. The gas is extracted through the bottom of the reactor and taken to a flare for final oxidation, after passing through a cyclone which separates the fine particles and a biomass filter that trap condensables in aerosol phase. The final stage of the work consist of the development and validation of a ASPEN PLUS model to simulate biomass gasification.